Complexities of coastal shark movements and their implications for management

Abstract

Global declines of shark populations are of concern because of their largely assumed role as moderators of ecosystem function. Without long-term data on movement patterns for many species, it is impossible to infer relative extinction risk, which varies as a function of range, dispersal and habitat specificity and use. The past 50 yr of research on coastal sharks has revealed common movement patterns among species. In the horizontal plane, measured home range size generally increases with body size. We demonstrate meta-analytically the effects of increasing body size and monitoring time on home range size. Changes in the extent of horizontal movement might arise from ontogeny, predator avoidance or environmental tolerances. In the vertical plane, movement patterns include oscillatory vertical displacement, surface swimming, diel vertical migration and swimming at depth. These vertical movements are often attributed to foraging or navigation, but have been quantified less than horizontal patterns. Habitat specificity is often correlated with environmental conditions such as depth, salinity, substratum, and in some cases, prey availability. Site fidelity is common in species that use nursery areas. However, fidelity to mating, pupping, feeding and natal sites has only been observed in a few species. To date, few studies have examined habitat partitioning, although some general patterns have emerged: habitats appear to be subdivided by benthos type, prey availability and depth. The conservation of coastal sharks can be facilitated in some cases by the use of marine protected areas, especially for coastal resident species using specific nursery, reproduction or feeding areas. Partial protected-area closures might be effective during aggregation or migration periods to protect older size classes, but these must be applied with other management strategies such as reduced fishing and size or bag limits to protect individuals throughout different life history phases. More long-term research on habitat use, migration patterns and habitat partitioning is essential for developing successful management initiatives for coastal shark populations.

Distributions of Sharks across a Continental Shelf in the Northern Gulf of Mexico

“…In the marine environment, distributions can be viewed in many dimensions. For sharks, studies of horizontal distribution abound while studies of vertical (i.e., depth) distribution have received less attention (Speed et al 2010). This is particularly true of coastal systems, which sharks are traditionally thought to inhabit early in their life history (Springer 1967).…”

Diet shift and site-fidelity of oceanic whitetip sharks Carcharhinus longimanus along the Great Bahama Bank

“…The driving forces of these movements are the subject of increasing research attention given the need to sustainably manage fisheries that exploit these species, coupled with the realization that migrations are likely to be affected by global climate change (Dulvy et al 2008, Block et al 2011. The migratory cycles of sharks that live primarily in neritic and coastal habitats often involve predictable and repeated movements between a series of geospatially fixed locations ('site-fidelity') (Hueter et al 2005, Speed et al 2010, Bond et al 2012, Feldheim et al 2014, Chapman et al 2015. In contrast, oceanic pelagic sharks often orient to mobile environmental features such as oceanographic fronts, although sitefidelity to fixed locations does occur in oceanic pelagic species that complete part of their life-cycle over the continental shelf, along the coast, or at offshore bathymetric features such as seamounts (Casey & Kohler 1992, Bigelow et al 1999, Litvinov 2008, Block et al 2011.…”

Two’s company, three’s a crowd: fine-scale habitat partitioning by depth among sympatric species of marine mesopredator

“…In the marine environment habitat preferences, for example for particular substrates, temperatures or depths, are fundamental drivers of species distributions, migrations and fine-scale movements (Speed et al 2010, Gouraguine et al 2011, Queiroz et al 2016. Consequently, an understanding of habitat preferences is essential when considering conservation strategies (Kaiser 2005, Speed et al 2010, Queiroz et al 2016.…”